Stacked die in die BGA package

ABSTRACT

Semiconductor devices and stacked die assemblies, and methods of fabricating the devices and assemblies for increasing semiconductor device density are provided.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 10/424,470, filed on Apr. 28, 2003, which is a division of U.S.patent application Ser. No. 10/068,159, filed on Feb. 5, 2002, presentlypending.

FIELD OF THE INVENTION

This invention generally relates to assembling and packaging multiplesemiconductor dies, and more particularly to a stacked multiple diedevice and methods for fabricating the device.

BACKGROUND OF THE INVENTION

Miniaturization of wireless products such as cellular phones andhandheld computers such as personal digital assistants (PDA), has driventhe increased demand for smaller component footprints, which in turnincreases the popularity of multi-chip stack BGA packaging. Mostmulti-chip packages involve stacking dies on top of each other by meansof adhesive elements. However, to achieve a low package height formulti-chip stacked die packages, a significantly reduced die thicknessis needed together with the use of special wire bond techniques toreduce the height of the wire bond loop height.

Thin die handling and the required special bonding techniques poses manychallenges to the assembly process. FIGS. 1-3 depict conventional waysof packaging a multi-chip stacked die package. As shown in FIG. 1, oneprior art package 10 includes two conventional stacked dies, the first(bottom) die 12 being surface mounted by means of an adhesive element 14to a substrate 16, and a smaller second (top) die 18 being mounted by asecond adhesive element 20 onto the active surface 22 of the bottom die12, each of the dies being wire bonded 24 to the substrate 16. FIG. 2illustrates a prior art stack die package 10 a in which the first(bottom) die 12 a is mounted to a substrate 16 a in a flip chipattachment, and the second (top) die 18 a is surface mounted to theinactive surface 26 a of the first die 12 a by means of an adhesiveelement 20 a and wire bonded 24 a to the substrate 16 a. FIG. 3 shows aprior art three-die stack BGA package 10 b in which the first bottom die12 b is mounted to a substrate 16 b by an adhesive element 14 b, asecond (middle) die 18 b is mounted on the active surface 22 b of thebottom die 12 b by a second adhesive element 20 b, and a third (top) die28 b is mounted on a spacer 30 b mounted on the active surface 32 b ofthe second (middle) die 18 b, with each of the dies being wire bonded 24b to the substrate 16 b.

In stacked die assemblies in which the bottom die is a flip chip, thereis a limit on the minimum overall thickness of the package that can beachieved. If a solder-bumped wafer having a 150 μm bump height were tobe ground to a total thickness of 150 μm to 200 μm, there would be ahigh occurrence of broken wafers due to the stress induced on the wafersfrom the bumps. Furthermore, even if the wafer does not crack, the diestrength will drop significantly due to the presence of “dimples” on thebackside of the wafer. Such dimples are typical defects observed on bumpwafers that are ground too thin or an inappropriate backgrinding tape isused in the process.

In addition, as depicted in FIG. 3, with multiple stacked dies, a spacer30 b is required to create the minimal clearance for the wire loopheight between the second (middle) die 18 b and the third (top) die 28b. This results in a higher package height, or requires ultrathin diesin order to meet the package height requirement. Thinner dies translateinto a higher possibility of cracked dies during the assembly process.

In view of these and other deficiencies, improvements in stacked diemodules are desirable.

SUMMARY OF THE INVENTION

The present invention provides semiconductor devices and stacked dieassemblies, methods of fabricating the devices and assemblies forincreasing semiconductor device density, and method of fabricating diepackages of the assemblies.

In one aspect, the invention provides a stacked die assembly. In oneembodiment, the stacked die assembly, comprises a first (bottom) diedisposed on a substrate, a bonding element connecting bond pads on anactive surface of the bottom die to terminal pads on the substrate, anda second die mounted on the bottom die. The second die has a bottomsurface with a recessed edge along the perimeter of the die thatprovides an opening for the bonding element extending from the bond padsof the bottom die, thus eliminating the need for a spacer between thetwo dies to achieve sufficient clearance for the bonding element. Asecond bonding element connects the bond pads on the active surface ofthe second die to terminal pads on the substrate. Adhesive elements aretypically disposed between the two dies and the bottom die and thesubstrate.

In another embodiment, the stacked die assembly, comprises a first(bottom) die disposed on a substrate, typically through a flip chipattachment, and having a recess formed in the upper (inactive) surface.A second die is at least partially disposed within the recess of thefirst die. A bonding element connects bond pads on the active surface ofthe second die to terminal pads on the substrate. An adhesive elementcan be disposed within the recess to attach the two dies. In a furtherembodiment of this assembly, a third die is mounted on the second die.The third die has a bottom surface with a recessed edge along theperimeter of the die that provides an opening for the bonding elementextending from the bond pads of the second die, thus eliminating theneed for a spacer between the two dies for clearance of the bondingelement. A second bonding element connects the bond pads on the activesurface of the third die to terminal pads on the substrate. An adhesiveelement can be used to attach the second and third dies.

In a further embodiment, the stacked die assembly, comprises a first(bottom) die disposed on a substrate, a bonding element connecting bondpads on the active surface of the first die to terminal pads on thesubstrate, and a second die mounted on the bottom die. A recess isformed on the bottom surface of the first die, and an adhesive elementis disposed within the recess to attach to the first die to thesubstrate. The containment of the adhesive element in the recess ratherthan being disposed between the die and the substrate as a separatelayer decreases the overall height of the die assembly. In an embodimentof this assembly, the second die has a recessed edge along the perimeterof the bottom surface for clearance of the bonding element extendingfrom the bond pads of the second die, thus eliminating the need for aspacer between the two dies. Bond pads on the second die are connectedto terminal pads on the substrate by a second bonding element, and anadhesive element can be used to attach the second and third dies.

In yet another embodiment, the stacked die assembly, comprises a first(bottom) die disposed on a substrate, typically through a flip chipattachment, and a second die having a recess formed in the bottom(inactive) surface. The first die is at least partially disposed in therecess of the second die, and a bonding element connects bonding pads onthe second die. An adhesive element can be disposed within the recess toattach the two dies.

In another aspect, the invention provides a semiconductor package. Invarious embodiments, the package comprises a stacked die assemblyaccording to the invention, at least partially encapsulated. The packagecan further include external contacts disposed on the second surface ofthe substrate for attaching the package as a component to an externalelectrical apparatus or device.

In another aspect, the invention provides methods of fabricating theforegoing stacked die assemblies and semiconductor packages.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings, which are forillustrative purposes only. Throughout the following views, thereference numerals will be used in the drawings, and the same referencenumerals will be used throughout the several views and in thedescription to indicate same or like parts.

FIGS. 1-3 depict cross-sectional, side elevational views of prior artembodiments of stacked die packages.

FIG. 4 is a cross-sectional, side elevational view of an embodiment of astacked die package according to the invention.

FIG. 5 is an enlarged partial view of the package of FIG. 4, showing therecessed edge and opening between the stacked dies.

FIGS. 6-11 illustrate sequential processing steps in the fabrication ofthe stacked die package of FIG. 4, according to an embodiment of amethod of invention. FIG. 6 is a bottom, perspective view of the seconddie of the package of FIG. 4, showing the removed (etched) portion ofthe die forming the recessed edge along the perimeter of the die. FIGS.7 and 9-11 are cross-sectional, side elevational views of sequentialsteps in the mounting of the dies. FIG. 8 is a top plan view of a panelwith multiple die packages disposed thereon.

FIG. 12 is a cross-sectional, side elevational view of anotherembodiment of a stacked die package according to the invention.

FIGS. 13-16 illustrate sequential processing steps in the fabrication ofthe stacked die package of FIG. 12, according to an embodiment of amethod of invention. FIG. 14 is a top, perspective view of the first(bottom) die of the package of FIG. 12, showing the recess formed in thedie. FIGS. 13 and 15-16 are cross-sectional, side elevational views ofsequential steps in the mounting of the dies.

FIG. 17 is a cross-sectional, side elevational view of anotherembodiment of a stacked die package according to the invention.

FIGS. 18-19 illustrate sequential processing steps in the fabrication ofa portion of the stacked die package of FIG. 17, according to anembodiment of a method of invention, showing the mounting of the third(top) die.

FIG. 20 is a cross-sectional, side elevational view of anotherembodiment of a stacked die package according to the invention.

FIGS. 21-24 illustrate sequential processing steps in the fabrication ofthe stacked die package of FIG. 20, according to an embodiment of amethod of invention. FIG. 22 is a bottom, perspective view of the first(bottom) die of the package of FIG. 20, showing the recess formed in thebottom surface of the die. FIGS. 21 and 23-24 are cross-sectional, sideelevational views of sequential steps in the mounting of the dies.

FIG. 25 is a cross-sectional, side elevational view of anotherembodiment of a stacked die package according to the invention.

FIGS. 26-29 illustrate sequential processing steps in the fabrication ofthe stacked die package of FIG. 25, according to an embodiment of amethod of invention. FIG. 26 is a bottom, perspective view of the second(top) die of the package of FIG. 25, showing the recess formed in thebottom surface of the die. FIGS. 27-29 are cross-sectional, sideelevational views of sequential steps in the mounting of the dies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described generally with reference to the drawingsfor the purpose of illustrating embodiments only and not for purposes oflimiting the same. The figures illustrate processing steps for use infabricating semiconductor devices in accordance with the presentinvention. It should be readily apparent that the processing steps areonly a portion of the entire fabrication process.

The terms “top” and “bottom”, and “upper” and “lower” are used hereinfor convenience and illustrative purposes only, and are not meant tolimit the description of the invention inasmuch as the referenced itemcan be exchanged in position.

The invention advantageously reduces the overall height of stacked diepackages, achieves a desirably low package profile, allows the use ofthicker dies in the stack assembly to reduce the number of cracked dies,eliminate the need for a spacer between dies to provide clearance forbond wires extending from an underlying die, and reduces the number ofpasses required for manufacturing multiple stacked dies by eliminatingthe need for mounting a spacer. The invention further offers morereliable adhesion bleed out control, and the benefits increase as moredies are stacked. The method of the invention can be utilized tofabricate an assembly comprising additional stacked die layers to thoseof the illustrated embodiments using the described concepts herein.

In each of the described embodiments, prior to mounting the individualdies of a stacked assembly, the backside (inactive surface) of a die(wafer) can be backgrinded or otherwise processed to a desiredthickness, flatness value and texture using conventional methods in theart.

Referring to FIG. 4, a first embodiment of a multiple chip die assemblypackage 40 according to the invention is depicted in a cross-sectional,side elevational view. The package 40 comprises a first (bottom) die 42mounted to a support substrate 44, and a second (top) die 46 mounted onthe bottom die 42. Bond pads 48 a, 48 b on the first and second dies 42,44 are wire bonded 50 a, 50 b, respectively, to terminal pads 52 a, 52 bon the support substrate 44. Substrate 44 further includes externalcontacts 54, for example, in the form of conductive solder balls, toconnect the die package 40 to an external electrical apparatus (notshown). As best seen in FIG. 5, a portion or thickness 60 (shown inphantom) along the perimeter 56 of the second (inactive) surface 58 ofthe second (top) die 46 is removed (e.g, etched) to provide a recess(recessed edge) 62. The recessed edge 62 has a height (h) and providesan opening 63 for sufficient clearance of the bond wires 50 a (or otherconnecting member such as TAB tape) extending from the bond pads 48 a onthe bottom die 42 to the substrate 44. This eliminates the need for aspacer (e.g., FIG. 3, 30 b) between the two overlying dies to providethe necessary clearance for bond wires extending from the lower die 42,and thus achieves a lower overall package height 67. Adhesive elements64, 66 can be utilized, respectively, to secure the bottom die 42 ontothe support substrate 44, and the second (top) die 46 onto the bottomdie 42.

FIGS. 6-11 illustrate an embodiment of a process flow and method forforming the stacked die package 40 of FIG. 4.

Prior to mounting, a portion or thickness of the second (inactive)surface 58 of the second (top) die 46 can be removed to form therecessed edge 62. As shown in FIGS. 5-6, a portion 60 (shown in phantomin FIG. 5) of the surface 58 has been removed along the perimeter 56 ofthe die. Known methods in the art can be used to selectively remove aportion 60 along the perimeter of the die 46 such that when the die 46is subsequently mounted onto the first (bottom) die 42, the recessededge 62 provides an opening with sufficient clearance for the bond wires50 a extending from the bottom die 42 to the support substrate 44. Therecessed edge 62 can be formed using known techniques in the art, forexample, a chemical wet etch or dry etch, laser ablation, or othermechanical means of reducing the bottom surface 58 of the top die 46 toa predetermined depth.

Referring now to FIGS. 7-9, the first (bottom) die 42 is mounted on afirst surface 68 of the support substrate 44. The bottom die 42comprises a first (active) surface 70 with a plurality of bond pads 48 aalong the periphery thereof, and a second (bottom) surface 72. As shownin FIG. 7, the bottom surface 72 of the bottom die 42 is aligned withand facing the first surface 68 of the support substrate 44 prior toassembly.

The support substrate 44 can comprise an electrically insulating polymermaterial such as a resin reinforced with glass fibers, for example,bismaleimide triazine (BT) resin, epoxy resins such as FR-4 or FR-5laminates, ceramics, and polyimide resins; a metal leadframe (e.g.,Alloy42 or copper); a flexible polyimide film (e.g., KAPTON from DuPont,Wilmington, Del., or UPILEX from Ube Industries, Ltd., Japan); amongother substrates. A representative thickness of the substrate is about50 μm to about 500 μm. As shown in FIG. 8, the support substrate 44 canbe in the form of a strip or panel 74 on which multiple die packages 40are formed, whereby the panel 74 can be singulated, for example, bycutting or shearing along an expansion slot 76, into individualpackages.

Referring to FIG. 7, the bottom die 42 can be attached to the supportsubstrate 44 by use of an adhesive element 64. The adhesive element 64can be applied onto the bottom surface 72 of the bottom die 42 (asshown), and/or to the first surface 68 of the support substrate 44. Theadhesive element 64 can comprise any suitable adhesive material known inthe art, including contact adhesives, thermoplastic adhesives andthermosetting adhesives, for example, a die-attach epoxy or equivalent,or a double-sided, multi-layered adhesive tape such as polyimide filmcoated on both sides with adhesive. The bottom die 42 and/or the supportsubstrate 44 can be provided in a pre-taped form with an adhesive tapeattached thereto, or an adhesive element 64 can be applied to either orboth of the bottom die 42 and the support substrate 44 duringfabrication of a stacked die package. Many suitable adhesive applicationmethods for liquid or gel adhesive application are known in the art,such as screen printing, roller applicator, spray, and transfer.Similarly, an adhesive tape may be applied from a dispenser and severedfrom a roll of tape, or applied from a transfer (carrier) film.

Referring to FIG. 9, with the first (bottom) die 42 mounted on thesubstrate 44, the bond pads 48 a of the first (bottom) die 42 are thenelectrically connected to the terminal pads 52 a on the supportsubstrate 44, for example, by wire bonding (as shown) or by tapeautomated bonding (“TAB”). For example, ball bonds (not shown) can bethermosonically bonded to the bond pads 48 a, and the bond wires 50 aextended and bonded to the terminal pads 52 a on the support substrate44. In other embodiments, TAB bonding and ultrasonic bonding, as knownin the art, can be used to connect the bond pads 48 a and the terminalpads 52 a.

Referring to FIGS. 10-11, the second (top) die 46 is then mounted ontothe first (active) surface 70 of the first (bottom) die 42 to form thestacked die assembly 78. The second die 46 comprises a first (active)surface 80 with a plurality of bond pads 48 b along the peripherythereof, and a second (inactive) surface 58. As shown in FIG. 10, thesecond surface 58 of the second (top) die 46 is aligned with and facingthe first surface 70 of the first (bottom) die 42 prior to assembly. Therecessed edge 62 between the first (bottom) die 42 and the overlyingsecond die 46 is sized with a height (h) to provide an opening 63 forsufficient clearance of the bond wires 50 a extending from the bottomdie 42 to the support substrate 44.

The second (top) die 46 can be attached to the bottom die 42 by means ofan adhesive element 66, for example, a tape or die-attach adhesive asdescribed with reference to adhesive element 64. The first (bottom) die42 and/or the second (top) die 46 can be provided in a pre-taped formwith an adhesive tape attached thereto, or an adhesive element 66 can beapplied to either or both dies during mounting of the second (top) dieonto the first (bottom) die.

As shown in FIG. 11, the bond pads 48 b of the second (top) die 46 arethen electrically connected to the terminal pads 52 b on the supportsubstrate 44, for example, by wire bonding, as shown in the illustratedexample, or by TAB bonding, resulting in the wire-bonded stacked dieassembly 78.

The die assembly 78 can be partially or fully encapsulated with adielectric encapsulation material 82, typically a thermoset resin, theassembly 78 can be encapsulated using known techniques in the art, forexample, screen printing, glob-top, pot molding, and transfer molding,resulting in the encapsulated stacked die package 40 depicted in FIG. 4.In one embodiment, a number of die assemblies 78 can be placed in alower mold plate or half of an open multi-cavity mold, one assemblywithin each cavity, and following encapsulation, the mold plates areseparated and the individual packages 40 can be singulated.

In the embodiment illustrated in FIG. 4, external contacts 54, typicallyin the form of conductive solder balls (or other suitable conductivematerial such as conductive epoxies or conductor-filled epoxies),columns, pins, and the like, are mounted on the second (bottom) surface84 of the support substrate 44 for electrical connection of the encaseddie package 40 as a component to an external electrical apparatus (notshown). Examples of such electric apparatus include a PCB or otherexternal circuitry (not shown) such as a motherboard of a computer,program logic controller (PLC), a testing apparatus, among others. Thesupport substrate 44 typically includes a variety of conductivethrough-holes or vias 86 that extend through the cross-section of thesubstrate and establish routing of the conductive elements through thesubstrate 44, and further include electrically conductive metal lines ortraces and pads formed on the second (bottom) surface 84 on which theexternal contacts 54 are mounted.

Where multiple die packages are fabricated on a panel substrate (e.g.panel 74, FIG. 8), the panel can be singulated into individual diepackages 40, for example, by cutting or shearing.

Another embodiment of a multiple chip die assembly package according tothe invention is depicted in a cross-sectional, side elevational view inFIG. 12. The package 40′ comprises a first (bottom) die 42′ mounted to asupport substrate 44′ in a flip chip attachment, and a second (top) die46′ mounted in a recess 88′ formed in the first (upper) surface 72′ ofthe bottom die 42′. Bond pads 48 b′ on the second (top) die 46′ are wirebonded 50 b′ to terminal pads 52 b′ on the support substrate 44′. Thesubstrate further includes external contacts 54′ (e.g. solder balls) forconnection of the die package 40′ as a component to an externalelectrical apparatus (not shown). The recess 88′ in the bottom die 42′allows the second (top) die 46′ to be inset into the bottom die 42′,thus achieving a lower overall package height 67′. An adhesive element66′ can be utilized to attach the second (top) die 46′ onto the bottomdie 42′.

FIGS. 13-16 illustrate an embodiment of a process flow and method forforming the stacked die package 40′ of FIG. 12.

FIGS. 13 and 15 depict simplified cross-sectional views of the mountingand bonding of the first (bottom) die 42′ in a flip chip attachment tothe substrate 44′. As shown, the first die 42′ comprises a first(active) surface 70′ and a second (inactive) surface 72′. The activesurface 70′ of the first die 42′ includes a plurality of bond pads withconductive bumps 90′ mounted thereon, which are arranged in apredetermined configuration. The conductive bumps 90′ typically comprisea metal or alloy such as copper, silver or gold, or a conductive polymermaterial, and can be formed by known methods in the art, for example,electroplating, metal stud bumping by wire bonders, and stenciling. Thesupport substrate 44′ can be in a form as described, for example, withrespect to the support substrate 44 (die package 40) (FIGS. 6-11).

Prior to mounting, a recess 88′ can be formed in the second (inactive)surface 72′ of the first (bottom) die 42′, as shown in cross-section inFIG. 13, and in a top perspective view in FIG. 14. The recess 88′ issized and configured to receive the second die 46′ therein in asubsequent step. The recess 88′ can be formed in any suitable shape,such as square, rectangular, oval, and circular. The recess 88′ can beformed to a predetermined depth and width to accommodate the placementof the second die therein using known methods in the art, for example,patterning and utilizing a chemical wet etch or dry etch, laserablation, or other mechanical means of removing the second (inactive)surface 72′ of the die. Dry etchers are commercially available, forexample, from SECON, having an etch rate of 25 μm/min. for an 8-inchwafer. The recess can be formed at the wafer level, the die level (i.e.,singulated die), or on a strip level after the die 42′ is mounted on thesubstrate (e.g., strip).

The bottom die 42′ can be mounted on the support substrate 44′ byconventional flip chip methodology. As shown in FIG. 13, the activesurface 70′ of the bottom die 42′ is aligned with and facing the first(upper) surface 68′ of the support substrate 44′ prior to assembly.Traces and electrical connections (not shown) on the first surface 68′of the support substrate 44′ are configured to correspond to theconfiguration of bond pads and the conductive bumps 90′ of the bottomdie 42′. The conductive bumps 90′ in the form of solder bumps can bereflowed to physically and electrically bond with the traces or otherconductive elements on the first (upper) surface 68′ of the supportsubstrate 44′, or cured in the case of conductive polymer bumps,although other methods such as thermal compression can also be used.Terminal pads 52 b′ on the first surface 68′ of the support substrate44′ are exposed along the periphery.

Referring to FIGS. 15-16, the second (top) die 46′ is then mounted inthe recess 88′ of the bottom die 42′. The second (top) die 46′ comprisesa first (active) surface 80′ with a plurality of bond pads 48 b′ alongthe periphery thereof, and a second (bottom) surface 58′. As shown inFIG. 15, the second (bottom) surface 58′ of the second (top) die 46′ isaligned with and facing the recess 88′ in the second surface 72′ of thebottom die 42′ prior to assembly.

The second (top) die 46′ can be attached to the bottom die 42′ by meansof an adhesive element 66′. The adhesive element 66′ can be appliedwithin the recess 88′ to the recess surface 92′ of the bottom die 42′,and/or to the second surface 58′ of the top die 46′ (as shown). Theadhesive element 66′ can comprise any suitable adhesive material knownin the art, for example, a tape adhesive or die attach adhesive, asdescribed with respect to adhesive element 64′. The adhesive element 66′can have a thickness such that it functions as a spacer to control thedegree of insertion of the second die 46′ into the recess 88′. The firstand/or second dies 42′, 46′ can be provided in a pre-taped form with anadhesive tape attached thereto, or an adhesive element 66′ can beapplied to either or both dies during fabrication of the stacked diepackage 40′. The adhesive element 66′ can be applied by conventionalmethods known in the art.

As depicted in FIG. 16, the bond pads 48 b′ of the second (top) die 46′are then electrically connected by wire bonds 50 b′ to the terminal pads52 b′ on the support substrate 44′, for example, by wire bonding (asshown) or by TAB bonding.

The wire bonded stacked die assembly 78′ can then be partially or fullyencapsulated with a dielectric encapsulation material 82′ using knownmethods in the art to form the encapsulated stacked die package 40′shown in FIG. 12.

External contacts 54′ (e.g., conductive solder balls can then be mountedon the second (bottom) surface 84′ of the support substrate 44′ forconnecting the die package 40′ to a motherboard or other electricalapparatus (not shown).

Where applicable, a panel substrate comprising a plurality of dies(e.g., FIG. 8, panel 74) can then be singulated into individual diepackages 40′.

A further embodiment of a multiple chip die assembly package accordingto the invention is depicted in a cross-sectional, side elevational viewin FIG. 17. The die package 40″ incorporates features of the diepackages 40, 40′ depicted in FIGS. 4 and 12.

As illustrated in FIG. 17, the package 40″ comprises a first (bottom)die 42″ mounted onto a support substrate 44″ in a flip chip attachment,and a second (middle) die 46″ at least partially received within arecess 88″ in the bottom die 42″, similar to the die package 40′ (FIG.12). The package 40″ further comprises a third (top) die 94″ mounted onthe first (active) surface 80″ of the second (middle) die 46″, similarto the die package 40 (FIG. 4). Bond pads 48 b″, 48 c″ on the second(middle) die 46″ and the third (top) die 94″ are wire bonded (50B″, 50c″) to terminal pads 52 b″, 52 c″, respectively, on the supportsubstrate 44″. Substrate 44″ further includes external contacts 54″(e.g., solder balls) for connecting the die package 40″ as a componentto an electrical apparatus (not shown). A portion along the perimeter ofthe second (inactive) surface 96″ of the third (top) die 94″ ispartially removed to provide a recessed edge 62″ to provide an opening63″ for sufficient clearance of the bond wires 50 b″ connecting the bondpads 48 b″ on the second (middle) die 46″ to the substrate 44″, thuseliminating the need for a spacer between the two dies 46″, 94″. Therecess 88″ in the bottom die 42″ allows the second (middle) die 46″ tobe inserted (nested) therein. The recess features 62″, 88″advantageously combine to achieve a lower overall package height 67″.Adhesive members 66″, 98″ can be utilized, respectively, to attach thesecond (middle) die 46″ to the bottom die 42″, and the third (top) die94″ to the second (middle) die 46″.

The stacked die package 40″ of FIG. 17 can be fabricated utilizing theprocess steps described above in fabricating packages 40, 40′.

Prior to mounting, the recesses 88″, 62″ can be formed in the first(bottom) die 42″ and the third (top) die 94″, respectively.

A recess 88″ can be formed in the second (inactive) surface 72″ of thebottom die 42″ (FIG. 18), as described with respect to die 42′ (package40) and as depicted in FIGS. 13-14. The recess 88″ is sized andconfigured to receive the second (middle) die 46″ therein in asubsequent step, and can be suitably shaped to correspond with the shapeof the second die.

A recessed edge 62″ along the perimeter 56″ of the second (inactive)surface 58″ of the third (top) die 94″ can be formed as describedpreviously for the second die 46 of package 40 and as depicted in FIGS.4-6. A portion 60″ of the third (top) die 94″ is removed along thesecond (bottom) surface 58″ to provide a recessed edge 62″.

Similar to the mounting of the first die 42′ on the substrate 44′ shownin FIGS. 13 and 15, the first (bottom) die 42″ is mounted on a supportsubstrate 44″ using flip chip technology, with the terminal pads 52 a″,52 b″ on the surface of the support substrate 44″ exposed along theperiphery.

The second (middle) die 46″ is then mounted in the recess 88″ of thebottom die 42″, as depicted in FIGS. 15-16. The second die 46″ comprisesa plurality of bond pads 48 b″ on a first (active) surface 80″, and asecond (bottom) surface 58″. The bottom surface 58″ of the second die46″ is mounted onto the recess surface 92″ of the bottom die 42″ bymeans of an adhesive element 66″, such as a tape or die-attach adhesiveas described with respective to adhesive element 64. The dies 42″, 46″can be pre-taped or an adhesive element 66″ can be applied to thesurface of either or both dies during fabrication of the package.

The bond pads 48 b″ of the second die 46″ are then electricallyconnected to the terminal pads 52 b″ on the support substrate 44″, forexample, by wire bonding or by TAB binding, resulting in a structuresimilar to that shown in FIG. 16.

Referring now to FIG. 18, the third (top) die 94″ can then be mounted onthe second (middle) die 46″ similar to the mounting of the second die 46on the bottom die 42 shown in FIGS. 10-11. The third (top) die 94″ ismounted onto the first (active) surface 80″ of the second die 46″ toform the stacked die assembly 78″, as depicted in FIG. 19. The third(top) die 94″ comprises a first (active) surface 100″ with a pluralityof bond pads 48 c″ along the periphery thereof, and a second surface 96″with recessed edge 62″. As shown in FIG. 18, the second surface 96″ ofthe third (top) die 94″ is aligned with and facing the first (active)surface 80″ of the second (middle) die 46″ prior to assembly.

The third (top) die 100″ can be attached to the second die 46″ by meansof an adhesive element 98″, for example, a tape or die attach adhesive,as described hereinabove with respect to adhesive element 64. The dies46″, 100″ can be provided in a pre-taped form or an adhesive element 98″can be applied to either or both dies during mounting of the third die94″ onto the second die 46″. The recessed edge 62″ of the third (top)die 94″ has a height (h″) to provide an opening 63′″ with sufficientclearance for the bond wires 50 b″ extending from the second die 46″ tothe support substrate 44″.

Referring to FIG. 19, the bond pads 48 c″ of the third (top) die 94″ arethen electrically connected to the terminal pads 52 c″ on the supportsubstrate 44″, for example, by wire bonding (50 c″) or TAB bonding.

The die assembly 78″ can be partially or fully encapsulated 82″resulting in the die package 40″ depicted in FIG. 17. External contacts54″ in the form of conductive solder balls (or other suitable conductivematerial or form) are mounted on the second (bottom) surface 84″ of thesupport substrate 44″ to provide electrical connection of the diepackage 40″ to an electrical apparatus (not shown). Thereafter, amulti-die panel can be singulated into individual die packages.

Referring to FIG. 20, another embodiment of a multiple chip die assemblypackage according to the invention is depicted in a cross-sectional,side elevational view. The package 40′″ comprises a first (bottom) die42′″ mounted to a support substrate 44′″, and a second (top) die 46′″mounted on the bottom die 42′″. The second die 46′″ comprises a first(active) surface 80′″ with bond pads 48 b′″ along the periphery thereof,and a second (inactive) surface 58′″. As illustrated, the second die46′″ is larger in size, i.e., a greater width (w) and/or length (l) thanthe bottom die (see FIG. 6). Bond pads 48 a′″, 48 b′″, on the first andsecond dies 42′″, 46′″ are wire bonded 50 a′″, 50 b′″ to terminal pads52 a′″, 52 b′″ on the support substrate 44′″, which further includesexternal contacts 54′″ to connect the die package 40′″ to an electricalapparatus. Similar to the die 46 depicted and described with respect toFIGS. 4-6, a portion of the second (inactive) surface 58′″ of the second(top) die 46′″ is removed to provide a recessed edge 62′″ for sufficientclearance for the bond wires 50 a′″ mounted on the underlying bottom die42′″. A cavity or recess 102′″ is also etched in the second (bottom)surface 72′″ of the bottom die 42′″, and is sized for receiving anadhesive element 104′″ therein to secure the bottom die 42′″ to thesupport substrate 44′″. The recess features 62′″, 102′″ combine toachieve a lower overall package height 67′″ for the package 40′″ byeliminating the need for a spacer between the top and bottom dies, andmounting the adhesive element 104′″ as an insert into the recess 102′″in the bottom die 42′″ rather than as a distinct layer between thebottom die 42′″ and the substrate 44′″. In addition, the recess 102′″contains a die-attach adhesive therein and limits the amount of adhesive(epoxy) bleed onto bond fingers and/or other components on the substrateadjacent to the die edge.

FIGS. 21-24 illustrate an embodiment of a method and process flow forforming the stacked die package of FIG. 20.

Prior to mounting, the recesses 102′″, 62′″ can be formed in the first(bottom) die 42′″ and the second (top) die 46′″, respectively.

As shown in FIG. 21, and in a bottom perspective view in FIG. 22, arecess 102′″ is formed in the second (bottom) surface 72′″ of the first(bottom) die 42′″. The recess 102′″ is sized and configured to receivean adhesive member 104′″ therein for attachment of the die 42′″ to thesubstrate 44′″. The recess 102′″ can be formed in any suitable shape,such as square, rectangular, oval, and circular. The recess 102′″ can beformed using known methods in the art, for example, patterning andutilizing a chemical wet etch or dry etch, mechanical drilling orpunching, and laser ablation of the second surface 72′″ of the die 42′″.The recess 102′″ can be formed at the wafer level or the die level(i.e., singulated die).

A recessed edge 62′″ along the perimeter 56′″ of the second (inactive)surface 58′″ of the second (top) die 46′″ can be formed as describedpreviously for the second die 46 (package 40) depicted in FIGS. 4-6. Aportion of the die 46′″ is removed such that, when the second die 46′″is then mounted onto the first die 42′″, the recessed edge 62′″ providesan opening 63′″ for sufficient clearance of the bond wires 50 a′″extending from the first die 42′″ to the terminal pads 52 a′″ on thesupport substrate 44′″.

Referring to FIG. 21, the second (bottom) surface 71′″ of the first(bottom) die 42′″ is aligned with and facing the first (upper) surface68′″ of the support substrate 44′″ prior to assembly.

The first die 42′″ is attached to the support substrate 44′″ by means ofan adhesive element 104′″. The adhesive element 104′″ can be applied tothe recess surface 106′″ of the recess 102′″ of the first (bottom) die42′″, and/or onto the first (upper) surface 68′″ of the substrate 44′″and aligned with the recess 102′″ to be received therein. The adhesiveelement 104′″ can comprise an adhesive gel or tape, as describedhereinabove with respect to adhesive element 64 (package 40). The firstdie 44′″ and/or the substrate 44′″ can be provided in a pre-taped form,or an adhesive element 104′″ can be applied to the surface of either orboth the first die 42′″ and the substrate 44′″ during the attachmentstep. The first die 42′″ is attached to the substrate 44′″ such that theterminal pads 52 a′″, 52 b′″ on the surface of the substrate areexposed.

Referring to FIGS. 23-24, the second (top) die 46′″ is then mounted ontothe first (bottom) die 42′″ to form the stacked die assembly 78′″. Asshown in FIG. 23, the second surface 58′″ of the second (top) die 46′″is aligned with and facing the first (active) surface 70′″ of the first(bottom) die 42′″ prior to assembly. The second (top) die 46′″ can beattached to the first die by means of an adhesive element 66′″, forexample, with a tape or die attach adhesive, as described with respectto the adhesive element 64 (die package 40). Either or both of the firstand second dies 42′″, 46′″ can be provided in a pre-taped form or theadhesive element 66′″ can applied to either or both dies during themounting step.

As depicted in FIG. 24, the bond pads 48 b′″ of the second (top) die46′″ can then be electrically connected to the terminal pads 52 b′″ onthe substrate 44′″. The recessed edge 62′″ of the second (top) die 46′″has a height (h′″) sufficient to provide an opening 63′″ for adequateclearance of the bonding wires 50 a′″ extending from the second die 46′″to the substrate 44′″.

The wire-bonded stacked die assembly 78′″ can be partially or fullyencapsulated with an encapsulant material 82′″ using known techniques inthe art to form the encapsulated stacked die package 40′″ as depicted inFIG. 20. Thereafter, external contacts 54′″ can be mounted on the second(bottom) surface 84′″ of the support substrate 44′″ for electricalconnection of the die package 40′″ to an external electrical apparatus(not shown).

Singulation of a multiple die panel or strip can then be performed toprovide individual die packages 40′″.

Referring to FIG. 25, a further embodiment of a multiple chip dieassembly package according to the invention, is depicted in across-sectional, side elevational view. The package 40″″ comprises afirst (bottom) die 42″″ mounted in a flip chip attachment to a supportsubstrate 44″″, and a larger sized, second (top) die 46″″ mounted on thefirst (bottom) die 42″″. Bond pads 48 b″″ on the second (top) die 46″″are wire bonded 50 b″″ to terminal pads 52 b″″ on the support substrate44″″. External contacts 54″″ are mounted on the second (bottom) surfaceof the substrate 44″″ for connecting the package 40″″ to an externalelectrical apparatus (not shown). A portion of the second (bottom)surface 58″″ of the second (top) die 46″″ is removed to provide a recess108″″ for receiving the bottom die 42″″ therein. The recess feature108″″ helps achieve a lower overall package height 67″″ for the package40″″ by nesting the first die 42″″ within the overlying second die 46″″.

FIGS. 26-29 illustrate an embodiment of a method and process flow forforming the stacked die package of FIG. 25.

Prior to mounting, the recess 108″″ can be formed in the second (bottom)surface 58″″ of the second (top) die 46″″, as shown in FIG. 25 and in abottom perspective view in FIG. 26. The recess 108″″ can be formed atthe wafer level or the die level. The recess 108″″ is sized andconfigured to receive the bottom die 42″″ therein, and can be formed inany suitable shape, such as square, rectangular, oval, and circularusing known techniques in the art.

As depicted in FIG. 27, the first (active) surface 70″″ of the first(bottom) die 42″″ is aligned with and facing the first (upper) surface68″″ of the support substrate 44″″ prior to assembly. The active surface70″″ of the first die 42″″ includes a plurality of bond pads withconductive bumps 90″″ mounted thereon, which are arranged in apredetermined configuration. The bottom die 42″″ can be mounted on thesupport substrate 44″″ according to conventional flip chip techniques,resulting in the structure shown in FIG. 28.

The second (top) die 46″″ is then mounted onto the first (bottom) die42″″ to form the stacked die assembly 78″″. The second die 46″″comprises a first (active) surface 80″″ with bond pads 48 b″″, and asecond (inactive) surface 58″″. As shown in FIG. 28, the second surface58″″ of the second (top) die 46″″ is aligned with and facing the secondsurface 72″″ of the first (bottom) die 42″″ prior to assembly. The first(bottom) die 42″″ is received at least partially in the recess 108″″ andcan be attached to the recess surface 106″″ of the second die 46″″ bymeans of an adhesive element 66″″ such as a tape or die attach adhesiveas described with respect to the adhesive element 64 (die package 40).Either or both of the first and second dies 42″″, 46″″ can be providedin a pre-taped form, or the adhesive element 66″″ can applied to eitheror both dies during the mounting step.

Referring to FIG. 29, the bond pads 48 b″″ on the first (active) surface80″″ of the second (top) die 46″″ can then be electrically connected tothe terminal pads 52 b″″ on the substrate 44″″.

Partial or full encapsulation of the die assembly 78″″ can be performedusing known techniques in the art to form the encapsulated package 40″″shown in FIG. 25. External contacts 54″″ can then be mounted on thesecond (bottom) surface 84″″ of the substrate 44″″ to facilitateelectrical connection of the component die package 40″″ to an externalelectrical apparatus (not shown).

Individual die packages of a multiple die panel (e.g., as shown withreference to panel 74 in FIG. 8) can be separated by a singulationtechnique.

Comparative Example 1 and Example 2

A comparison of the package design shown in FIG. 2 (prior art) with thepackage design shown in FIG. 12.

FIG. 2 FIG. 12 Bottom die, thickness 6 mils 6 mils Second die, thickness6 mils 6 mils Bond line, thickness 1 mil  1 mil  Slot (recess) depth — 4mils Overall total thickness of the 13 mils  9 mils stacked dies

By utilizing a package design according to the invention, a lowerpackage height can be achieved using thicker dies. In addition, thickerdies can be utilized to help reduce the number of cracked dies thatoccur during the assembly process.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A die assembly, comprising: a die situated on a substrate with asurface of the die defining a recess proximal to said substrate, saidrecess defined by at least two sides.
 2. The device of claim 1, whereinthe recess is defined by five sides.
 3. A die assembly, comprising: afirst die situated on a substrate with a surface defining a recessproximal to said substrate, said recess defined by at least two sides;and a second die situated on the first die, second die defined by planesthat form a non-rectangular shape.
 4. A die assembly, comprising: afirst die situated on a substrate with a surface defining a recessproximal to said substrate, said recess defined by at least two sides;and a second die situated on the first die, second die defined by planesthat form a non-rectangular shape.
 5. A die assembly, comprising: a diesituated on a substrate, said die defined by planes that form anon-rectangular shape, wherein the die defines a recess around an entireperiphery and in a side in a region distal from circuitry of the seconddie.
 6. A die assembly, comprising: a die situated on a substrate, saiddie defining an inner cavity in a side in a region distal from circuitryof the die.
 7. The die assembly of claim 6, wherein the inner cavity isexposed with the die situated on the substrate.
 8. The die assembly ofclaim 7, further comprising a die situated within the cavity of the diemounted on the substrate.
 9. The die assembly of claim 6, wherein theinner cavity is within a side of the die situated on the substrate. 10.The die assembly of claim 9, further comprising an adhesive elementsituated within the cavity of the die.
 11. The die assembly of claim 9,further comprising a second die situated within the cavity of the die.12. A method of fabricating a semiconductor device, comprising: mountinga surface of a die on a substrate, said surface of the die comprising arecess defined by at least two sides.
 13. The method of claim 12,wherein the recess is defined by five sides.
 14. The method of claim 12,wherein the die has a height, and an adhesive element is situated on thesubstrate within said recess and does not increase the height of thedie.
 15. A method of fabricating a semiconductor device, comprising:mounting a surface of a first die on a substrate, said surface of thefirst die comprising a recess defined by at least two sides; andmounting a second die on the first die, wherein the second die definesplanes that form a non-rectangular shape.
 16. The method of claim 15,wherein the second die defines a recess around an entire periphery andin a side in a region distal from circuitry of the second die.
 17. Themethod of claim 15, wherein the second die defines an arch in across-section.
 18. The method of claim 15, wherein the second diedefines a T-shape in a cross-section.
 19. A method of fabricating asemiconductor device, comprising: mounting a die on a substrate, saiddie defining planes that form a non-rectangular shape, wherein the diedefines a recess around an entire periphery and in a side in a regiondistal from circuitry of the second die.
 20. The method of claim 19,wherein the die defines an arch in a cross-section.
 21. The method ofclaim 19, wherein the die defines a T-shape in a cross-section.
 22. Amethod of fabricating a semiconductor device, comprising: mounting a dieon a substrate, wherein said die defines an inner cavity in a side in aregion distal from circuitry of the die.
 23. The method of claim 22,wherein the inner cavity is exposed with the die mounted on thesubstrate.
 24. The method of claim 23, further comprising mounting a diewithin the cavity of the die mounted on the substrate.
 25. The method ofclaim 22, wherein the inner cavity is within a side of the die mountedon the substrate.
 26. The method of claim 25, further comprising, priorto mounting the die on the substrate, mounting a second die within thecavity of the die.